Chromosomal aberrations, cell suppression and oxidative stress generation induced by metal oxide nanoparticles in onion (Allium cepa) bulb

Abstract

There has been rapid increase globally in the production of functionally divergent nanoparticles in recent times. The uncontrolled discharge of such nanomaterials is a serious threat to the environment. We assess the impact of various-sized metal oxide nanoparticles (MONPs) on cell cycle progression and induction of oxidative stress in onions. Of these, CuO-NPs and TiO₂-NPs significantly reduced the mitotic index (MI) by 28% and 17%, respectively, whereas Al₂O₃-NPs augmented the MI by 13% compared to untreated onion roots. The NPs internalization into the root tissues followed a dose dependent fashion. Also, several types of chromosomal aberration such as bridges, stickiness, vagrant, broken, and lag chromosomes were noticed. The reactive oxygen species activity of roots growing under CuO-NPs, Al₂O₃-NPs, and TiO₂-NPs was significantly increased by 58, 30, and 10%, respectively. The superoxide dismutases activity (U g⁻¹ FW) of roots increased from 2.4 ± 0.4 (control) to 6.1 ± 0.8 (CuO-NPs), 4.1 ± 0.2 (Al₂O₃-NPs) and 2.9 ± 0.2 (TiO₂-NPs), whereas, catalase activity (mmoles min⁻¹ g⁻¹ FW) was recorded as 18.5 ± 2.1 (CuO-NPs), 15 ± 1.1 (Al₂O₃-NPs) and 13.8 ± 1 (TiO₂-NPs) against 11.4 ± 1 (control). The formazan formed due to superoxide (O₂˙⁻) reaction with nitroblue tetrazolium showed a dose dependent increase in roots treated with Al₂O₃-NPs and TiO₂-NPs. Interestingly, under CuO-NPs exposure, the absorbance was considerably high at 200 μg ml⁻¹ which dropped at 2000 μg ml⁻¹ suggesting a clear attenuation of O₂˙⁻ by superoxide scavenging enzymes. The present findings provide base line data for better understanding of the mechanistic basis of phytotoxicity of MONPs to onion plants which can further be extended to other vegetable crops.